Prestressed concrete pipes

ABSTRACT

In a prestressed concrete pressure pipe it is known to have the tensioned wire wrapping around a concrete pipe core terminate short of the bars outside joint-sealing surface at the end of the pipe core, embedded pretensioned wires extending axially of the core, and a tensioned ring either within or outside of the unwrapped or bare end of the core. In the present invention end portions of the pretensioned wires are bent outwardly at a hoop towards the unwrapped surface of the core and the hoop is pretensioned by the wires. The stress in the wires is thereby utilized to impart radially inwardly directed forces emanating from the bent-out portions of the wires and from the hoop to restrain flaring and cracking of the unwrapped end of the core.

United States Patent 11 1 Bald PRESTRESSED CONCRETE PIPES [75] Inventor:Robert E. Bald, Roseland, NJ.

[73] Assignee: Interpace Corporation, Parsippany,

22 Filed: Apr. 29, 1974 21 Appl. No.: 465,341

[52] US. Cl 138/176; l38/DIG. 5

[51] Int. Cl. F16L 9/08 [58] Field of Search 138/174-176, 138/DIG. 5;264/228 [56] References Cited UNITED STATES PATENTS 2,805,683 9/1957Kennison 138/176 X $034,536 5/1962 Kennison 138/176 3,034,537 5/1962Seaman et a1. 138/176 3,258,033 6/1966 Ohnstad 138/176 PrimaryExaminer.lohn W. Huckert Assistant Examiner-Charles Gorenstein Attorney,Agent, or FirmGeorge F. Des Marais ABSTRACT In a prestressed concretepressure pipe it is known to have the tensioned wire wrapping around aconcrete pipe core terminate short of the bars outside jointsealingsurface at the end of the pipe core, embedded pretensioned wiresextending axially of the core, and a tensioned ring either within oroutside of the unwrapped or bare end of the core. In the presentinvention end portions of the pretensioned wires are bent outwardly at ahoop towards the unwrapped surface of the core and the hoop ispretensioned by the wires. The stress in the wires is thereby utilizedto impart radially inwardly directed forces emanating from the bent-outportions of the wires and from the hoop to restrain flaring and crackingof the unwrapped end of the core.

4 Claims, 6 Drawing Figures US. Patent Oct. 14, 1975 5% mm W PRESTRESSEDCONCRETE PIPES This invention relates to prestressed concrete pressurepipe in which pretensioned wires extend longitudinally of the wall of amonolithic concrete pipe core, and the core is circumferentiallycompressed by a highly tensioned wire wrapping. The core commonly has atleast one end finished as a spigot adapted for entering a complementaryouter member for forming a joint therewith.

It would be desirable to have the spigot end of the tensioned wirewrapping terminate immediately adjacent the end face of the pipe core ifit were not of importance that a finite length of the outer surface ofthe core be left bare in order to seat a gasket against the concrete ofthe core for sealing a joint with an outer joining pipe member, such asa bell of another pipe, or a coupling sleeve. The end of the tensionedwire wrapping at the spigot is therefore anchored short of the surfacewhich is provided for seating the gasket. Because of this, residualstresses caused by the tensioned wire wrapping remain in the concrete ofthe unwrapped spigot portion of the pipe core.

It is not unusual that the residual stresses resulting from thetensioned wire wrapping are high enough to overcome the strength of thecore beyond the wrapping irrespective of that portion of the strengthwhich is derived from the axial compressive effect of axially extendingprestressed wires in the wall of the core. A consequence of residualstresses is that the spigot end of the core flares outwardly and ringcracks can develop at the inside of the core in the vicinity of thespigot end of the tensioned wire wrapping. Various efforts have beenmade to eliminate flexural cracking of the nature mentioned asdisclosed, for example, in the U.S. Pat. Nos. 3,034,537 and 3,183,0l 1.

One proposed mode for suppressing flaring and cracking invokes the useof a tensioned auxiliary wire binding about the spigot between the endface of the spigot and its gasket-receiving surface, but this entailssupplemental winding and fastening procedures and requires that the maintensioned wire wrapping around the core be anchored more distant fromthe end face of the core than should be necessary.

Another mode for inducing circumferential compression in the spigot endof a concrete core is to form a ring at the ends of the longitudinallyprestressing wires by interlinking loops at their ends with loops ofother wires to which force was applied to tension the prestressing wiresbefore the core was moulded. That mode is not sufficiently trustworthybecause of the uncertainty of the amount of tension that can be imposedin the formed ring and, in any case, the construction would have limitedapplication to the manufacture of pressure pipe for which prestressingwires of relatively light weight would be appropriate.

In accordance with the present invention end portions of longitudinallyprestressing wires or rods which enter the spigot of a pipe core engagea hoop and are angularly inclined outwardly from the hoop to their endswhich are closer to the end face and the outer surface of the spigotthan the hoop. The longitudinal reinforcing for the core thus sets up apattern of resisting forces in the concrete of the core at its spigotend which includes (a) axial compression, (b) radial bending stress atthe end with the tension side at the external surface of the core andthe compression side at the internal side, and (c) circumferentialcompression of the core near its end due to strain in the tensionedhoop. The strength of the spigot end of the core is thereby increased inproportion to the stresses resulting from the three force systems.

The resisting forces developed in the core varies with the stress in theprestressing wires and the angle which the deflected portion of eachwire makes with the axially extending portion of the wire.

The highest radial thrust component derivable from deflected portions ofthe prestressing wires is obtainable with the deflected portionsdisposed perpendicularly to the axis of the core. In practice the angleof deflection should be within a range of about 15 to and preferably aswide as the class, size and wall thickness of a pipe will permit.

According to one aspect of the present invention there is provided amoulded concrete pipe core with a spigot having an annular surface forengaging joint sealing means, a tensioned wire wrapping subjecting thecore to circumferential compression, said wrapping having an endanchored short of said joint sealing means surface, said core containinga plurality of pretensioned wires spaced apart circumferentially of saidcore and extending substantially the length of the core, a hoopcontained in the concrete of said core, said hoop substantiallyconcentric to the axis of said core and located axially inward from theend face of the core at the spigot end of the core, said pretensionedwires engaging the inside of said hoop and having portions thereofdeflected radially outwardly from their points of engagement with saidhoop and towards said end face at the spigot end of the core.

Other aspects of the invention will be particularly pointed out in theclaims appended hereto. The invention itself as to its objects andadvantages, and the manner in which it may be carried out, will bebetter understood by referring to the following description and theaccompanying drawing forming a part thereof.

In the drawing, FIG. 1 illustrates a pipe employing the invention withparts cut away for showing interior portions thereof;

FIG. 2 is a sectional view of an end portion of a mould on line 22 ofFIG. 4;

FIG. 3 is a section of an end portion of a mould on line 3-3 of FIG. 4;

FIG. 4 is an end view of a segment of a mould end ring;

FIG. 5 is a profile of the spigot of a different pipe core; and

FIG. 6 is a profile of the spigot of still another form of a pipe core.

The concrete pressure pipe illustrated in FIG. 1 comprises a mouldedconcrete pipe core 10 which is reinforced and longitudinaly compressedby a plurality of prestressed wires 11 embedded in and bonded to theconcrete of the wall of the core at equal intervals circumferentiallyaround the core. The wires are of high tensile strength steel and theends of each wire extend close to the respective end faces 12 and 13 ofthe core. As shown in the drawing, nuts 14 and 15 are attached tothreads impressed into each wire, but other supplementary anchoringmeans may be used.

The left end of the pipe is fashioned as a spigot of sufficient lengthfor entering into a bell of another pipe or other complementary memberfor making a joint therewith. There may be a spigot at each end of apipe, or

a spigot at one end and a bell at the other end which, in the pipe shownin FIG. 1, is a steel bell ring 16.

The spigot includes a flange 17 having an annular recess 18 forreceiving a joint sealing means, such as a rubber gasket, and providingan annular surface 19 on the concrete core onto which the gasket may beseated.

The pretensioned wires 11 are bonded to the concrete of the core. Thewires engage the inside of a pretensioned hoop 20 contained in the core.At the points of engagement of the wires with the hoop the end portionsof the wires are directed angularly outwardly from their longitudinallydisposed portions. The hoop is constructed from one or several rings ofa high tensile strength steel wire, the ends of which are spliced tocomplete the hoop.

The hoop 20 is subjected to tangential tension when the wires 11 aretensioned in a mould before the mould is filled and the concrete hardensto form the core. When the core is formed and removed from the mould theinwardly directed force of the hoop is resisted by the concrete of thecore.

A tensioned wire wrapping 21 extending between the fixed anchorages 22and 23 circumferentially compresses the core and the bell ring of thepipe. The wrapping is applied in a manner known in the art by helicallywinding a tensioned high tensile strength steel wire around the core andthe bell ringafter the core has been thoroughly cured.

The spigot end of the wire wrapping at the anchorage 22 is necessarilylocated a short distance from the end face 12 of the core in order toleave bare an outside surface of the core for seating the sealing meanswhich subsequently will be used to seal a joint with another pipe. Amortar or other protective coating 24 covers the full length of thetensioned wire wrapping 21. The edge 25 of the coating forms a side wallat one side of the gasket-bearing surface 19.

The pipe core is moulded in a rotatable cylindrical mould of which twodifferent sections through an end ring 26 are shown in FIGS. 2 and 3.Another end ring (not shown) is mounted to the other end of acylindrical shell 27 which forms the outside central wall of the mould.As thus constituted the mould is adapted for moulding in accordance withthe roller suspension machine moulding technique, but the core can beformed in a centrifugal machine or other suitable mould.

Each wire 11 is engaged by a detachable gripper 28 threaded on the wireand having a head 29 which bears on the end ring 26. The far end of eachwire is also engaged by a similar gripper which is supported by the endring at that end of the mould.

The hoop 20 is placed in the mould to the outside of the wires 11 beforethe ends of the wires are gripped. It is held spaced from the insideradial surface 30 of the ring 26 by a number of tie-wires 31, one ofwhich is shown in FIG. 3. An end of each of the wires 31 is twistedaround and lashed securely to the hoop, and the other end of the wire isgripped by a removable anchoring pin 32 which is supported on the mouldring 26.

Each individual prestressing wire 11 is initially stressed under ameasurable tension prerequisite for meeting the specifications for aparticular pipe design. The number of longitudinal wires used in a coreis dependent upon variable factors such as their size, the size and wallthickness of the core, the beam and crushing loading of a known expectedearth cover and the maximum internal water pressure expected for aparticular job. For a 48-inch diameter core designed to contain 28% inchprestressing wires about seven equally distributed tie-wires 31 sufficefor retaining the hoop in position when the prestressing wires aresubjected to tension in the mould, but more or less would serve equallywell.

Upon initially tensioning the wires 11 by applying traction to theirgrippers at one end of the mould, a radial outward component of theapplied tension is exerted on the engaged hoop 20 and the hoop isthereby subjected to a high tangential tension which subsequently exertscircumferential compression on the concrete of the core when the core isstripped of the mould.

After the mould has been filled with concrete and the concrete issufficiently cured, all of the grippers are removed. Upon removal of thegrippers 28 the radial outward restraint of the mould on the bent-outportions of the wires is transferred from the mould onto the concrete ofthe core. Thus the bent-out portions of the wires exert radially inwardforces on the spigot end of the core which are effective to represscircumferential expansion or flaring of the spigot end of the core whenthe tensioned wire wrapping 21 is applied.

In FIG. 5 there is shown the profile of the spigot end of anotherconcrete pipe core 33 having a relatively wide flange 34 and an annulargasket-receiving recess 35 with side walls constituted of the materialof the core. The terminal coil 36 of the tensioned wire wrapping 37 islocated adjacent the flange and the pretensioned hoop 38 is located inor near the diametrical plane of the terminal coil.

Tension was applied to the prestressed hoop 38 and the prestressed wires39 in the manner previously described. In this modification the bond ofthe concrete to the wires is relied on for maintaining the wires andtheir deflected portions 40 stressed in tension. Should the pipe designand pressure requirements warrant, the ends of the deflected portionsmay be provided with anchoring means, either inside or outside of thecore.

FIG. 6 shows an application of the invention in a concrete pipe corehaving a straight-walled spigot 41 and an O-ring gasket 42 resting in agroove formed in the core. In this type of pipe the terminal coil 43 ofthe tensioned wire wrapping 44 is more removed from the end face 45because a longer exposed surface of the core is needed to accommodate asocket of a joining pipe. The hoop 46 is located within the wall of thepipe as close to the end face as practicable. The presence of thepretensioned hoop and of the deflected portions 47 of the pretensionedreinforcing wires 49 and their reaction on the concrete inhibits thecracking of the concrete at the inside of the spigot.

The invention results in strengthening the spigot and effecting economyin the manufacture of any type of prestressed concrete pressure pipehaving a circumferentially compressed concrete core with an exposed orbare surface at the spigot and compressed longitudinaIly by pretensionedwires or rods.

The invention may also be practiced if the various wire elements in theconcrete pipe were replaced with equivalent high strength materials suchas strands of glass filaments or fibers.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined in the following claims:

l. A prestressed concrete pressure pipe comprising a moulded concretepipe core with a spigot having an annular surface for engaging jointsealing means, a tensioned wire wrapping subjecting the core tocircumferential compression, said wrapping having an end anchored shortof said joint sealing means surface, said core containing a plurality ofpretensioned wires spaced apart circumferentially of said core andextending substantially the length of the core, a pretensioned hoopcontained in the concrete of said core, said hoop substantiallyconcentric to the axis of said core and located axially inward from theend face of the core at the spigot end of the core, said pretensionedwires passing through said hoop in engagement with the inside of saidhoop said pretensioned wires having bends at the points of engagementwith said hoop from which portions of the wires continuing straight fromsaid bends towards said end face of the core are inclined from theirpoints of engagement with said hoop radially outwardly relative to theaxis of said core whereby said inclined wire portions provide stresssystems reacting radially inwardly onto the adjacent concrete of thecore and together with said stressed hoop exert restraint againstflaring of the spigot end of the core which otherwise could be caused bysaid tensioned wire wrapping.

2. A prestressed concrete pressure pipe according to claim 1, whereinsaid spigot includes a flange with said joint sealing means surface atthe outside thereof.

3. A prestressed concrete pressure pipe according to claim 1 includinganchoring means attached to the ends of said pretensioned wires.

4. A prestressed concrete pressure pipe according to claim 1, whereinsaid hoop is located from said end face a distance substantially equalto the spacing of the spigot end of said wire wrapping from said endface.

1. A prestressed concrete pressure pipe comprising a moulded concretepipe core with a spigot having an annular surface for engaging jointsealing means, a tensioned wire wrapping subjecting the core tocircumferential compression, said wrapping having an end anchored shortof said joint sealing means surface, said core containing a plurality ofpretensioned wires spaced apart circumferentially of said core andextending substantially the length of the core, a pretensioned hoopcontained in the concrete of said core, said hoop substantiallyconcentric to the axis of said core and located axially inward from theend face of the core at the spigot end of the core, said pretensionedwires passing through said hoop in engagement with the inside of saidhoop said pretensioned wires having bends at the points of engagementwith said hoop from which portions of the wires continuing straight fromsaid bends towards said end face of the core are inclined from theirpoints of engagement with said hoop radially outwardly relative to theaxis of said core whereby said inclined wire portions provide stresssystems reacting radially inwardly onto the adjacent concrete of thecore and together with said stressed hoop exert restraint againstflaring of the spigot end of the core which otherwise could be caused bysaid tensioned wire wrapping.
 2. A prestressed concrete pressure pipeaccording to claim 1, wherein said spigot includes a flange with saidjoint sealing means surface at the outside thereof.
 3. A prestressedconcrete pressure pipe according to claim 1 including anchoring meansattached to the ends of said pretensioned wires.
 4. A prestressedconcrete pressure pipe according to claim 1, wherein said hoop islocated from said end face a distance substantially equal to the spacingof the spigot end of said wire wrapping from said end face.